Dielectric ceramics, multilayer ceramic capacitor and method for manufacturing the same

Abstract

Crystal grains mainly composed of barium titanate have a mean grain size of not more than 0.2 μm. The volume per unit cell V that is represented by a product of lattice constant (a, b, c) figured out from the X-ray diffraction pattern of the crystal grains is not more than 0.0643 nm3. Thereby, a dielectric ceramics having high relative dielectric constant can be obtained. A multilayer ceramic capacitor comprises a capacitor body and an external electrode that is formed at both ends of the capacitor body. The capacitor body comprises dielectric layers composed of the dielectric ceramics, and internal electrode layers. The dielectric layers and the internal electrode layers are alternately laminated.

Description

[0001]Priority is claimed to Japanese Patent Application No. 2004-312454 filed on Oct. 27, 2004, and Japanese Patent Application No. 2004-340347 filed on Nov. 26, 2004, the disclosure of which is incorporated by reference in its entirety.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates to a dielectric ceramics, a multilayer ceramic capacitor using the same and a method for manufacturing them.[0004]2. Description of Related Art[0005]In recent years, as mobile devices such as cellular phones are more widely used and semiconductor devices that are the main part of a personal computer have higher speed and higher frequency, a multilayer ceramic capacitor for these electronics is increasingly required to have small size and large capacity.[0006]To meet such requirement, in a multilayer ceramic capacitor (MLC), efforts have been made for smaller size and larger capacity, by making dielectric layers thinner to enhance electrostatic capacity and ...

AI Technical Summary

Benefits of technology

The present invention relates to a new method for manufacturing a dielectric ceramic with high relative dielectric constant and excellent temperature characteristics. The ceramic is composed of crystal grains with a high relative dielectric constant, even in small thickness. The ceramic has a mean grain size of not more than 0.2 μm and contains crystal grains mainly composed of barium titanate. The ceramic can be used in a multilayer ceramic capacitor with high reliability and stability. The method involves obtaining dielectric primary powder with a small grain size, drying and heating it with a zeolitic drying agent, and molding it into a predetermined shape. The multilayer ceramic capacitor has alternating layers of dielectric layers and internal electrodes, with the dielectric layers composed of the dielectric ceramic described above. The ceramic has a high relative dielectric constant, excellent temperature characteristics, and insulation properties. The manufacturing process involves using a specific dielectric powder with a small grain size and a specific glass powder with a softening point and thermal expansion coefficient within certain ranges.

Problems solved by technology

Therefore, there has been a problem that a dielectric ceramics prepared by using the dielectric powder so obtained has a low relative dielectric constant.

However, if fine barium titanate powder according to Japanese Unexamined Patent Publication No. 2003-309036, for example, is used to make dielectric layers thinner in manufacturing a multilayer ceramic capacitor, abnormal grain growth occurs during firing at atmospheric pressure.

Therefore, crystal grains constituting a dielectric layer cannot have uniform grain size, and large crystal grains resulting from grain growth are present in part.

There has been a problem that a multilayer ceramic capacitor having such crystal grains has larger temperature characteristic of relative dielectric constant and lower insulation, in particular, lower reliability in high temperature load test.

Images